Propeller



Jan. 16, 1934. I I J. H, WILLIAMSON 1,943,571

PROPELLER Filed Oct. 22. 1931 Patented Jan. 16, 1934 UNITED STATES PATENT OFFICE PROPELLER James H. Williamson, Little Falls, N. J.

Application October 22, 1931.

11 Claims.

This invention relates, generally, to propellers; and the invention has reference, more particularly, to a novel construction of propeller adapted for general use.

b Propellers as heretofore generally constructed are known to produce air-streams or blasts which have varying velocities at varying radial distances from their rotating axes. The air-stream produced by the average propeller has a very low or even a negative velocity in the vicinity of the hub at. the rear of the propeller and a gradually increasing velocity as the radial distance from the hub increases until the tip portion of the propeller blade is approached, whereupon the velocity again falls substantially. The ordinary propeller in operation forces or draws air radially outwardly from the hub of the same and also forces or draws air radially inwardly from the tip of the same. These oppositely directed streams of air meet intermediate the length of the propeller blades and fiow together rearwardly from the blades in a direction substantially parallel to the axis of revolution of the propeller. I In other words, the propeller operates to produce a hollow cylinder of high velocity air surrounding and spaced from the axis of rotation of the propeller. This hollow cylinder or vortex of rapidly moving air sur rounds a region of reduced pressure which ex- 9 tends rearwardly of the hub of the propeller and is in turn surrounded by a region "of reduced pressure extending from the area swept over by the outer portions of the propeller blades. Eddy currents having a circular motion are set up in the regions of reduced pressure by the rapidly moving vortex of air, causing a considerable loss of energy due to air friction.

Thus, in producing this vortex or cylindrical hollow column of air, the propeller blades create considerable turbulence in the region rear of the tip portions of the blades and in the region rearof the hub area, which turbulence is energy consuming and greatly detracts from the efliciency of the propeller. Some of the air which flows outwardly from the hub of the propeller does not join the main vortex of rearwardly flowing air, but is sucked back toward the hub of the propeller owing to the region of reduced pressure to the rear of the hub. This produces auxiliary air streams which are merely eddy currents circulating around and around without doing any useful work though absorbing considerable energy from the propeller. The same is true of a portion of the radially, inwardly flowing 5 air at the tip portions of the propeller blades, A

Serial No. 570,315

portion of this inwardly flowing, radially moving air does not join the vortex moving rearwardly from the propeller, but is sucked back and outwardly from the vortex owing to the region of reduced pressure immediately behind the tips of the blades. These eddy currents are circulatory currents and do no useful work but greatly reduce the efficiency of the propeller. Various means have been used to counteract the eddy currents or turbulence in the region rear of the propeller hub and in the region rear of the propeller blade tip portion. This means often consists of bafiles or obstructions, which tend to reduce the flow of such eddy currents.

The principal object of the present invention is to provide a novel propeller which is so designed as toproduce an air-stream of substantially solid cylindrical shape, the cross-section of which air-stream has a diameter which is substantially equal to the diameter of the propeller, the velocities of air taken at consecutive varying radial distances from the center of the propeller to the tip thereof being all positive and of but gradually varying magnitudes, so that eddy currents or turbulence in the rear of both the hub area and blade tip area are substantially eliminated, thereby resulting in high operating eiiiciency.

Another object of the present invention lies in the provision of a novel propeller having a hub portion which is designed to draw air in toward the center of the propeller to thereby eliminate any tendency for a region of reduced pressure to exist in the central portion of the air stream produced by the propeller.

Still another object of the present invention is to provide a novel propeller of the above character, the blades of which are relatively wide adjacent the hub thereof and taper off substantially uniformly toward their tips, the relatively great width or cord length of the propeller blades adjacent the hub of the propeller providing a large operating area for enhancing the effective thrust of the propeller adjacent its hub, which enhanced thrust is desirable owing to the relatively slow movement of these inner portions of the blades as compared with those further out.

Still another object of the present invention lies in the provision or" a novel propeller having blade tip portions of greater pitch than the remainder of the blades whereby radial inflow of air at the tip portions is prevented, and the air is caused instead to flow" directly rearwardly from the propeller tip portions in a direction parallel to the axis of rotation of the propeller. 110

Still another object of the present invention is to provide a novel propeller of the above character which is of simple, sturdy construction and has a maximum emciency over a wide range of speeds, the said propeller being exceedingly quiet in operation.

Other objects of this invention, not at this time more particularly enumerated, will be clearly understood from the following detailed description of the same.

The invention is clearly illustrated in the ac companying drawing, in which:

Fig. 1 is a view in elevation of the novel propeller embodying the principles of the present invention.

Fig. 2 is a view looking at the right of the structure shown in Fig. 1.

Fig. 3 is a sectional view taken along line 3-3 of Fig. 1.

Fig. 4 is a sectional view taken along line 4.- l of Fig. 1. 1

Fig. 5 is an enlarged sectional view taken along line 5-5 of Fig. 2;

Fig. 6 is a perspective view of the propeller; and

Fig. '7 is a fragmentary enlarged view taken along line 7-7 of Fig. 2.

Similar characters of reference are employed in all of the above described views, to indicate corresponding parts.

Referring now to said drawing, the reference numeral 1 designates the novel propeller of this invention as a whole. This propeller is illustrated as having two blades, but it is to be un derstood that the invention is equally adaptable to propellers having three, four or even more blades. The hub of the propeller has fiat front and rear surfaces '7 and 8, respectively, which surfaces are perpendicular to the longitudinal axis of bore 9 of the propeller. The front surface '7 has a peripheral edge or boundary line consisting of two similar cambered curves 10 positioned on opposite sides of an imaginary diametric line, which line is illustrated by dot and dash lines in Fig. l and is designated 6. These cambered boundary curves 10 have the same contour as that of an aerofoil or the upper surface of an airplane wing. The leading end of each curve 10, i. e. the forward end as the propeller advances, terminates in the leading edge 12 of one propeller'blade, whereas the trailing end of the respective curve 10 is tangent to and merges into the leading edge 12 of the other propeller blade. The rear surface 8 also has a peripheral edge or boundary line consisting of two similar cambered curves 10 positioned on opposite sides of an imaginary diametric line.

The outer surface portions of the hub which extend from the marginal lines 10 and merge into the oppositely extending propeller blades 11 are also cambered substantially along imaginary helical lines similarly to that of an aerofoil. This is especially illustrated in Figs. 1, 2 and 5. wherein the hi h portions of the hub cambered surfaces are designated by the reference numeral 14. It will be noted that the high portions 14 are positioned fairly near the leading edges 12 of the propeller blades, and these high portions of the hub camber are in effect, continuations of the high portions 15 of the cambered blades 11. The low portions 16 of the hub cambered surfaces are at the trailing edges of the propeller blades and are relatively close to the central longitudinal axis of the hub, as especially illustrated in Figs. 2 and 5.

It will thus be noted that the outer surfaces of the hub are cambered, which camber extends from the front of the propeller to the rear thereof, the same having its high portion near the front of the hub and its low portion at the rear wall 8 thereof, causing the hub in use to throw air inwardly from around the front portion of the hub toward the center of the propeller and to discharge the same at the rear of the hub close to the propeller shaft in the same manner that an aerofoil draws air in toward the trailing edge thereof. The leading and trailing edges of the propeller blade converge toward each other, as illustrated in Fig. 1, so that though the blade adjacentthe hub is relatively wide, the tip portion 17 of the blade is relatively narrow. This construction is desirable in order to obtain a substantially uniform velocity of airstream output over the entire diameter of the propeller. Since the portions of the propeller blades near the hub move at a much slower speed than the tip portions 17, it is necessary that the inner portions of the blades be of increased width, so as to act for a longer time upon the air, to thereby develop the same velocity of air-stream as created by the narrow tip portions 17 moving at a faster speed.

As especially illustrated in Figs. 4 and 6, the blade pitch of the tip portions 17 is greater than that of the remainder of the blades. In other words, the pitch of the blades is substantially constant from the hub to the tip portion, but at the tip portion the pitch is increased, or in other words the angle between the tip portion 17 and a plane passing at right angles through the axis of the propeller is greater than the angle between this plane and the remaining portion of the propeller blades. The purpose of the increased pitch of the tip portion 17 is to off-set radial inflow of air which is present in normal propellers. This increased pitch has the effect of tending to direct air radially outwardly, which tendency is sufiicient to overcome the radial inward flow of air so that theair will actually pass directly rearwardly away from the tips of the propeller in lines parallel to the rotating axis of the same. This construction is contrary to the popular manner of designing propeller blades, wherein the tendency has been to decrease the pitch of the blade in proportion to the-distance of any portion of the blade from the hub so as to thereby maintain a substantially constant stress over all portions of the blade. The effect of this common reduction in pitch is to produce, in operation, a substantial radial inward flow of air, such as shown in Fig. 3 of the patent to Carter, Reissue No. 16,387 of July 20, 1926, resulting in objectionable eddy current losses. As has heretofore been explained, this radial inward flow of air from the blade tip portions toward the hub is just as objectionable as the radial outward flow of air from the hub toward the intermediate portions of the propeller blades and results in low propeller efficiency.

In operation, the propeller of this invention revolves in the direction indicated by the arrows in Figs. 1 and 5, presenting cambered surfaces to the air as the same advances. Not only are the blades themselves cambered, thereby offering a minimum of resistance to motion, but the hub portion is cambered with the trailing edge thereof close to the axis of the propeller at the rear of the hub, whereby air in the region of the propeller hub is drawn from the front of the propeller radially inwardly and rearwardly and is discharged so as to flow parallel to the hub andclose thereto, thereby preventing the formation of any regions of reduced pressure adjacent the rear portion of the hub, which would tend to create eddy currents and consequent loss of efficiency. The main portion of the blades extending between their tip portions and the hub, being of substantially fixed pitch and having a variable cord width which decreases in proportion to the distances from the propeller axis, will produce an air-stream of substantially uniform velocity throughout the cross-sectional area thereof, which velocity will be directed along lines parallel to the rotating axis of the propeller. The tip portions 1'7 of the blades being of greater pitch than the remaining portions of the blades, overcome the tendency for radial inward flow of air to take place, while at the same developing a rearwardly directed air-stream having a velocity substantially equal to that of the adjacent blade "peller of this invention produces a solid airstream of remarkably uniform velocity throughout the cross-sectional area thereof, which crosssectional area extends the full width of the propeller, whereby voids or areas of reduced pressure are eliminated, thereby substantially doing away with propeller drag and obtaining a very high efficiency in operation. In fact, these blades are so efficient in use, that they are being used successfully in duct lines where blowers have heretofore been used exclusively.

The novel propeller of this invention is remarkably quiet in operation and has been used successfully for many purposes where noise is objectionable. The elimination of eddy currents and burbling in the air-stream is largely the cause of quiet operation of the present propeller.

It will be noted that owing to the tapering of the propeller blades toward their tips in the manner shown in the drawing, a radial line extending from the hub to any point in a blade will lie wholly within the blade. In other words there is a direct physical connection along a radial line between any particle ofmass of the blades and the hub, so that there are no portions of the blades not directly supported against the action of centrifugal force. In ordinary blades having overhanging portions not sup-' ported by direct radial connection with the hub, vibration and noise as well as blade distortion, especially in the region of the blade tip, is created in operation owing to the presence of such overhanging portions.

Also, the blades of the propeller of this invention are exceedingly strong and are not flexed in use since they have their maximum width and consequent strength adjacent the hub where the maximum torque stress occurs in use. The disposition of the metal of the blades adjacent the hub overa long chord length extending angularly to the axis of the hub is such as to cause the blades to possess great rigidity, thereby eliminating fiexure of the tip portions of the blades in use.

The points of maximum thickness of each blade lie along a substantially straight line extending outwardly from the hub of the propeller. Inasmuch as the portions of the blades near the hub move relatively slow, the points of maximum blade thickness in these portions of the blades are positioned at a greater percentage of the chord lengths away from the leading edge, for efficient operation, than are'the points of maximum blade thickness in faster moving portions of the blades more removed from the hub. Thus, in Fig. 1 the dot and dash lines 18 may'designate imaginary lines overlying points of maximumblade thickness in the blades of the propeller.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it intended that ail matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is: l

1. A propeller comprising a hub having outer surfaces cambered after the manner of an aerofoil, the aerofoil camber of said hub outer surfaces extending helically about the rotating axis of said propeller, and blades extending outwardly from said hub, said blades having forward surfaces merging into the cambered outer surfaces of the hub.

2. A propeller comprising a hub having outer surfaces cambered after the manner of an aerofoil, the aerofoil camber of said hub outer surfaces extending helically about the rotating axis of said propeller, and blades extending outwardly from said hub, said blades having cambered forward surfaces merging into the cambered outer surfaces of the hub, the-high portions of the cambered hub surfaces being positioned adjacent the front of the propeller and the low portions thereof being positioned at the rear of said hub.

3. A propeller comprising a hub having outer surfaces cambered after the manner of an aerofoil, the aerofoil camber of said hub outer surfaces extending helically about the rotating axis of said propeller, the leading edges of said hub cambered surfaces being positioned at the front of the propeller and the trailing edges of said surfaces being positioned at the rear of the propeller, and blades extending outwardly from said hub, said blades having cambered forward surfaces merging into said cambered hub surfaces.

4. A propeller comprising a hub having flat front and rear surfaces and cambered outer surfaoes the aerofoil camber of said hub outer surfaces extending helically about the rotating axis of said propeller, the high portions of said cambered outer surfaces being positioned adjacent the front surfaces of said hub and the low portions of said cambered outer surfaces being positioned adjacent the rear surface of said hub, and blades extending, outwardly from said hub, the leading edges of said blades being tangent to peripheral edge portions of said hub front surface.

5. A propeller comprising, a hub having front and rear surfaces extending substantially perpendicularly to the rotating axis of the propeller, the peripheral edge of said front surface being defined by two similarly curved lines situated on opposite sides of a diametric line of said hub, said similar lines having the contours of outer surfaces of varying radii as measured from the propeller axis of rotation, the radii of said surfaces being greater adjacent the front of said hub than at the rear thereof, the outer ends of radii, disposed along helical lines about the rotating axis, of said propeller, lying along an aerofoil curve, whereby air is drawn inwardly from around the front of said hub and discharged at the rear thereof close to the axis of revolution of said propeller, and blades extending outwardly from said hub, said blades having tip portions of greater pitch than the remaining portions of said blade.

7. A propeller comprising a hub having curved outer surfaces of varying radii as measured from the propeller axis of rotation, the radii of said surfaces being greater adjacent the front of said hub than at the rear thereof, the radii disposed in helical planes about the propeller axis of rotation having their outer ends lying along aerofoil curves, whereby air is drawn inwardly from around the front of said hub and discharged at the rear thereof close to the axis of revolution of said propeller, and blades extending outwardly from said hub, said blades having a maximum width near said hub and decreasing in width in proportion to the distance from said hub, the tip portion of said blades having a pitch which is greater than that of the remainder of said blades, whereby radial inward flow of air along said tip portions is substantially eliminated.

8. A propeller comprising a hub and blades extending outwardly from said hub, said blades having a maximum cord length adjacent said being relatively wide near said hub and tapering toward their tip portions, the material of said blades being so disposed, that a radial line, extending from any point of said blades to said hub, lies substantially wholly within the bodyof said blades.

10. A propeller comprising, a hub and blades extending outwardly from said hub, said blades being relatively wide near said hub and tapering toward their tip portions, the forward surfaces of said blades being cambered after the manner of an aerofoil, the point of maximum thickness of any section of each blade being located at a greater percentage of the width of the section from the leading edge thereof than are points of maximum thickness of blade sections that are further removed from the propeller hub.

11. A propeller comprising a hub and blades extending outwardly from said hub, said hub having its outer surface cambered after the manner of an aerofoil along helical lines extending from the front to the rear of the hub intermediate adjacent blades.

JAMES H. WILLIAMSON. 

